1. Field of the invention
The present invention relates to a tree shear for felling trees and to a tree harvester having a tree shear-and-grapple head incorporating the aforesaid tree shear.
2. Description of the prior art
Known tree shears of the type to which the invention relates comprise a pair of shear blades that are pivoted, by powerful hydraulic jacks, like the two blades of scissors. When applied about the trunk of a tree to be felled and at its butt end, the sharp edges of the blade elements are forced into the trunk until the tree is severed from its base. The shearing pressure that must be applied to achieve felling has to be considerable since the knives or blade elements have to cut across the fibres of the tree trunk. In fact, severing of the tree is due to crushing as well as to shearing of the fibres. Now, this crushing action does not take place only in the shear plane but extends appreciably beyond that plane and, as a consequence, a not negligible part of the lower end of the tree is irremediably damaged insofar as using that part for making lumber boards is concerned.